The in vitro activities of cefixime, a new third-generation cephalosporin, and of 18 other antimicrobial agents against 18 strains of Helicobacter pylori were determined. The strains of H. pylori were isolated from gastric biopsy specimens and tested for sensitivity to antibiotics by an agar dilution technique under microaerophilic conditions. Among cephalosporins, cefixime had the highest antibacterial activity, with a MIC for 90% of strains (MIC(90)) of 0.125 mg/l. Josamycin and erythromycin, aminoglycosides and the penicillin group tested were comparatively less active (MIC(90) < or = 0.5 mg/l). Ofloxacin (MIC(90) 0.5 mg/l), ciprofloxacin (MIC(90) 0.125 mg/l) and the monobactam aztreonam (MIC(90) 4 mg/l) were also active. All isolates were susceptible to rifampicin (MIC(90) 1 mg/l) and resistent to cephalothin, cefsulodin and pefloxacin.